Micro-electromechanical systems (MEMS) include miniaturized mechanical and electromechanical elements that are made using micro-fabrication techniques. The physical dimensions of MEMS devices vary from well below one micron to several millimeters. Also, MEMS devices vary from relatively simple structures having no moving elements to extremely complex electromechanical systems having multiple moving elements under the control of integrated electronics. Functional elements of MEMS devices include miniaturized structures, micro-electronics, and micro-sensors and micro-actuators that convert energy from one form to another, such as a measured mechanical signal into an electrical signal. MEMS devices include pressure sensors, accelerometers, gyroscopes, microphones, digital mirror displays, and micro fluidic devices, and MEMS devices can be very sensitive to changes in critical dimensions of the devices.
Typically, MEMS accelerometers behave like a damped mass on a spring. When an accelerometer experiences acceleration, the mass is displaced to the point that the spring is able to accelerate the mass at the same rate as the casing. This displacement is measured to give the acceleration. Piezoelectric, piezoresistive, and capacitive components can be used to convert the mechanical motion into an electrical signal.
Some MEMS accelerometers include a proof mass and electrodes that face each other across a small gap. On one side of the gap are rotor electrodes arrayed on the proof mass or rotor. On the other side of the gap are stator electrodes or fixed electrodes, facing the moving rotor electrodes across the gap. Under the influence of external accelerations, the proof mass deflects from its neutral position and the capacitance between the rotor electrodes and the stator or fixed electrodes can be measured to determine the acceleration.